solar powered UAV, the mass and structural dynamics characteristics of solar powered UAV with different layouts and different structure forms in time and frequency domain are studied in this paper. Firstly, the thin-walled structure models of solar powered UAV with flying wing layout and diamond wing layout are established with the same solar panel laying area. The flutter characteristics are calculated by P-K method in frequency domain, and the response characteristics of the structure under dynamic loads are calculated in time domain. The dynamic characteristics and mass characteristics of solar powered UAV with large aspect ratio with different layouts are compared. Then, the rhombus grid structure is applied to the wing structure, and the finite element model of the rhombus grid structure is established to study the structural dynamics and mass characteristics of the diamond wing layout solar powered UAV. The results show that the frequency domain and time domain methods can accurately obtain the structural dynamic characteristics. The flutter characteristics and gust response characteristics of the solar powered UAV with diamond wing layout are better than those with flying wing layout, but the mass of diamond wing layout solar powered UAV is too large. The rhombus grid structure diamond wing layout solar powered UAV has good structural stiffness and higher flutter speed, and its structural mass is 21.5% lighter than that of the thin-walled diamond wing layout solar poWered UAV.

Geometric errors are caused due to the inaccuracy of machine components’ manufacturing and assembling, and significantly impact the dimensional precision of workpieces. Many researches have researched the methods of inversely identifying geometric errors of multi-axis milling machines from the workpiece profile, but those methods are inapplicable to identify geometric errors of ultra-precision lathe. This paper presents a new approach to research the inverse identification of geometric errors from the surface topography of workpiece for an ultra-precision lathe. First, a volumetric error model is built to analyze tool position errors caused by geometric errors. Next, a matrix decomposition method is put forward to simplify the calculation of tool position errors and describe the propagation process of geometric errors during the manufacturing process. This method decomposes final tool position errors into a sum of three components, and each has a definite geometric meaning. Then, an equivalent machining model is constructed to identify crucial geometric errors from the surface topography of workpiece. Geometric errors in this model can be worked out precisely through topography data sampled along a radial path on workpiece surface. Finally, some simulation experiments are implemented to verify the precision of matrix decomposition method and one plane surface is machined to validate the effectiveness of equivalent machining model.

The H-type gantry stage (HGS) is widely used in electric vehicle manufacturing and other fields. However, resulting from the existence of mechanical coupling, the synchronous control problem of HGS always troubles many engineers. Most synchronization schemes were either engaged in improving each motor’s tracking performance or committed to pure motion synchronization only. However, tracking and synchronous performance are interconnected, because of the mechanical coupling. In this paper, a rigid assumed system model of HGS, concerning the effects of mid-beam rotary inertia, mid-beam stiffness, and end-effector movement, is presented. Based on the proposed model, an adaptive robust synchronous control based on a rigid assumed model (ARSCR) is proposed to improve both synchronous and tracking performance of the HGS. From the Lyapunov analysis, the proposed ARSCR can achieve the convergence of synchronous error and tracking error, simultaneously. An HGS driven by dual linear motors is built and used to perform the experimental verification. The experimental results indicate the effectiveness of the proposed method.

The ram speed of a steam hammer is an important parameter that directly affects the forming performance of forgers. This parameter must be monitored regularly in practical applications in industry. Because of the complex and dangerous industrial environment of forging equipment, non-contact measurement methods, such as stereo vision, might be optimal. However, in actual application, the field of view (FOV) required to measure the steam hammer is extremely large, with a value of 2⁻3 m, and heavy steam hammer, at high-speed, usually causes a strong vibration. These two factors combine to sacrifice the accuracy of measurements, and can even cause the failure of measurements. To solve these issues, a bundle-adjustment-principle-based system calibration method is proposed to realize high-accuracy calibration for a large FOV, which can obtain accurate calibration results when the calibration target is not precisely manufactured. To decrease the influence of strong vibration, a stationary world coordinate system was built, and the external parameters were recalibrated during the entire measurement process. The accuracy and effectiveness of the proposed technique were verified by an experiment to measure the ram speed of a counterblow steam hammer in a die forging device.

Geometric errors remarkably affect the dimensional accuracy of parts manufactured by ultra-precision machining. It is vital to consider the workpiece shape for the identification of crucial error types. This research investigates the prioritization analysis of geometric errors for arbitrary curved surfaces by using random forest. By utilizing multi-body system (MBS) theory, a volumetric error model is initially established to calculate tool position errors. An error dataset, which contains information of 21 geometric errors, workpiece shape, and dimensional errors, is then constructed by discretizing the workpiece surface along the tool path. The problem of identifying crucial geometric errors is translated into another problem of feature selection by applying random forest on the error dataset. Moreover, the influence extent of each geometric error on the dimensional accuracy of four typical curved surfaces is analyzed through numerical simulation, and crucial geometric errors are identified based on the proposed method. Then, an iterative method of error compensation is proposed to verify the reasonability of the determined crucial geometric errors by specifically compensating them. Finally, under compensated and uncompensated conditions, two sinusoidal grid surfaces are machined on an ultra-precision lathe to validate the prioritization analysis method. Findings show that the machining accuracy of the sinusoidal grid surface with crucial geometric error compensation is better than that without compensation.

Conventionally, the dynamic modeling of H-type gantry stage(HGS) assumes that the stiffness of mid-beam is extremely high so that its deformation is ignorable. This assumption apparently simplifies the study, but unavoidably compromises the modeling precision as it is not consistent with the real working status especially at high frequency motion. Comparing with similar studies on moving mass problems, the beam vibration of HGS is excited not only by the moving mass and system acceleration but also by the non-synchronized motion of the two moving ends of mid-beam. Therefore, the objective of this paper is to propose an assumed mode method based on simplified mode shapes(AMM-SMS) by simultaneously considering the lateral flexibility and the motion of the ends of mid-beam. The proposed AMM-SMS adopts the mode shapes of a simplified system, which has the same geometry boundary condition(BC) with the investigated system, to discretize the nonlinear kinematic equations of the proposed system. This method improves the modeling precision with low complexity, and can be applied in different BCs of FHGS. The proposed method is verified by various comparisons with the finite element method. Based on the AMM-SMS, the first three natural frequencies and mode shapes are studied. The open-loop responses of the system are obtained to analyze the effects of different BCs, of the motion of end-effector and of the external exciting force on the vibratory behavior.

High-resolution imaging devices are of interest in the development of accurate 3D vision systems. However, it is challenging to achieve a balance between the image capturing speed and resolution. The image capturing speed is relatively low for high-resolution imaging devices, which restricts their applications in high-speed 3D measurements. Therefore, a low-speed-camera-array imaging method for high-speed 3D deformation measurements is proposed. Compared with existing methods using high-speed imaging devices, it has the advantages of low cost and high flexibility achieved by combining low-speed cameras into a stereo camera array high-speed imaging system. In order to achieve accurate 3D measurements, a bundle-adjustment-principle-based system calibration method is proposed. Four experiments, including an accuracy experiment, repeatability experiment, vibration measurement of a plastic board, and out-of-plane displacement measurement of rotating blades, demonstrated the accuracy and effectiveness of the proposed method. (C) 2018 Elsevier Ltd. All rights reserved.

High-altitude and long-endurance solar-powered UAV mostly uses the high-aspect-ratio wing. The tip of the wing is very deformed and the flutter velocity is low, which is easily affected by the gust load. The structural safety of UAV flying in the sky is a popular and difficult issue, but there is no design criterion for the structural design of the solar powered UAV. Therefore, in this paper, according to the structural characteristics of large aspect ratio solar powered UAV, the design criteria of structural safety are put forward, and the structure of solar powered UAV is studied respectively from static strength, stiffness and dynamic load. Numerical results show that under cruising condition, the maximum stress of solar powered UAV structure is much lower than the breaking strength of the material, but the sustained vibration caused by the flutter will cause a large overload, which will lead to fatigue and impact damage to the structure. Under the gust response, the structure response converges quickly, but after exceeding a certain flight speed, any gust will cause the structure to diverge and the structure to break down rapidly. At the same time, it can also be seen that the bending, twisting and horizontal waving of the large aspect ratio wing lead to structural flutter destruction.

Aiming at the problem of energy storage during the level flight of solar powered UAV, the energy management of UAV in horizontal flight is studied in this paper based on a diamond wing solar powered aircraft with dihedral. The incident angle from the sun to the solar cell can be derived from the relationship between the motion attitude of the aircraft and solar normal line, and then the energy production model coupled with the motion attitude is obtained, which is verified through the level flight. Besides, in order to maximize the residual energy, the energy production model and energy consumption model are combined to optimize the flight trajectory during the level flight. Finally, the simulation results show that the optimized trajectory can manage the energy better, which means that the residual energy can been maximized.

3D vision system becomes a critical tool in wind tunnel experiment. However, in hypersonic wind tunnel vibration is unavoidable, it will disturb the pose of cameras in vision system and heavily decrease the measurement accuracy. Aiming at solving this problem, an accurate and stable two-step self-calibration method is proposed. Firstly, a stable and fast non-iterative method is adopted to calculate the initial value of camera pose. Then, a globally convergent orthogonal iterative algorithm is used to obtain an accurate solution. According to the experiment results, the 3D vision system with self-calibration method can get accurate measurement results in hypersonic wind tunnel. And we applied the 3D vision system to measure the deformation of an aircraft wing model in hypersonic wind tunnel of China Aerodynamics Research and Development Center successfully.

This paper presents a method to identify lying automatically using EEG signals. The wavelet entropy of event-related potentials (ERP) carries information about the degree of order associated with a multi-frequency brain electrophysiological activity. We used wavelet entropy to analyze ERP during a lying task. Ten subjects were divided into guilty and innocent groups randomly. They were instructed to make a truthful or deceptive responses on the stimuli. EEG recordings on Pz channel were collected and the features of wavelet entropy were extracted. Statistical result reveals that there is significantly lower wavelet entropy value for the guilty group than that for the control group. We concluded that guilty subjects showed much high order degree of the brain state than normal persons after about 300 ms after stimulus onset. Hence, wavelet entropy is an effective and reliable approach to detect deception, and can help us to understand cognition processing deeply for lying behaviors.

This paper addresses the dynamic modeling and synchronous control for the RF Target Motion Simulators(RF TMS). The investigated TMS is used to simulate the target moving a wide range along x and y directions. The y-axis that moving along x directions is driven by two parallel linear motors which are arranged at both ends of y-axis. A mathematical model about the TMS is built using the Lagrangian equation. From the analysis of the model, it is the target motion along y directions that causes the two linear motors to be out of sync. To reduce the synchronization errors of dual linear motors, the effect of target movement on the dual linear motors is seen as disturbance and a sliding mode control(SMC) strategy with two-input-two-output is designed for the dual linear motors. Furthermore, the cross-coupled control(CCC) with PD controller is also studied as a comparison. A simulation process is implemented to verify the effect of proposed control method.

3D Visual Inspection for high-temperature objects has attracted more and more attention in the industrial and manufacture field. Until now it is still difficult to measure the shape of high-temperature objects due to the following problems: 1) the radiation and heat transfer through the air seriously affect both human and measurement equipment, so the manual measurement is not capable in this situation. 2) Because of the difficulties to handle the surfaces of the hot objects, it is hard to use artificial markers to align different pieces of data. In order to solve these problems, an automatic 3D shape measurement system for high-temperature objects is proposed by combing an industrial robot with a structured blue light 3D scanner. In this system, the route for inspection is planned with the cooled object and then executed automatically with the same object in hot state to avoid artificial operations. The route is carefully planned to reduce the exposure time of the measurement equipment under the high-temperature situation. Then different pieces of data are pre-mapped during the planning procedure. In the executing procedure, they can be aligned accurately thanks to the good repeatability of the industrial robot. Finally, different pieces of data are merged without artificial markers and the results are better than methods with traditional hand-eye calibration. Experiments verify that the proposed system can conduct the inspection of forging parts under the temperature of 900 degrees C and the alignment precision is 0.0013rad and 0.28mm.

Trajectory tracking control for linear oscillating motor is critical to improve the performance of linear electro-hydrostatic actuator (LEHA). However, both structured uncertainties (i.e., parametric uncertainties) and unstructured uncertainties (i.e., unmodeled dynamics, external disturbances, nonlinear friction) exist in LEHA may severely deteriorate the control performance of the system. In this paper, a control strategy which integrates adaptive robust control (ARC) and extended state observer (ESO) together is proposed to handle both structured and unstructured uncertainties. The proposed control strategy takes the advantages of ARC and ESO, which nullifies the disadvantages of ARC and ESO as well, guarantees accurate high-frequency trajectory tracking performance. In addition, a second-order system model is established by adapting dipole cancellation method and dominant pole theory before the design procedure of the controller. The simulation results are presented to verify the effectiveness and the achievable excellent performance of the proposed control strategy.

Distributing coded targets on the measured object is a reliable and common method for achieving optimum target location and accurate matching of corresponding targets among multi-view images. The circular coded targets which based on a central circular target surrounded by a coded band is widely used in vision measurement. However, it is difficult to decode the coded target while the number of pixels in the coded band is small or the projection angle is large. Aiming at solve this problem, a detection algorithm using the gray gradient to get the central angles of each coded section was proposed. In this algorithm, an accurate ellipse detection which can get sub-pixel locations was adopted to extract ellipse centers, and some false ellipses whose error in the fit of best fit is large will be rejected. Then, gray gradients in the coded band are calculated to get the central angle of each coded section, and the coded target will be decoded accurately. The experiment results show that the algorithm can locate and identify coded targets accurately under complex measurement conditions.

This paper proposes a simple synchronous control scheme for a linear servo system applied to driving the horizontal axis of far-field target motion simulators(TMS). The investigated horizontal axis is driven by two parallel linear motors, which are arranged at both ends of the vertical axis. This layout, which can improve the system dynamics, overall thrust and structural stiffness, requires accurate synchronous control. To meet this requirement, the velocity difference compensation scheme is proposed to reduce the synchronous errors. Prior to this, the parallel synchronous control model of dual linear motors is established, and a stiffness coefficient is introduced to consider the impact of the mechanical connection coupling between these two linear motors. The performance of the proposed method is verified by a S-curve motion profile, and the simulation results substantiate the effectiveness of the control method.

In recent years, the development of aircraft design and the high requirements of aircraft combat missions come up with new requirements for the aircraft's aerodynamic design. In this paper, the development process and existing problems of aeroelasticity in recent years are reviewed. Besides, related researches are cited to elaborate the effect of the aircraft geometric nonlinearity and composite material on aeroelasticity of aircraft, especially high-aspect-ratio aircraft and military/civilian aircraft. Finally, the application of CFD on nonlinear aeroelasticity are illustrated.